The present invention relates to a rustproof control valve and a variable displacement compressor having the rustproof control valve.
Generally, in a variable displacement compressor, pressure in a crank chamber or crank chamber pressure is determined based on a balance between the amount of refrigerant gas flowing from a discharge pressure region to the crank chamber through a supply passage and the amount of refrigerant gas flowing from the crank chamber to a suction pressure region through a bleed passage. Pressure differential between the crank chamber and cylinder bores is varied by varying the crank pressure. Thereby the inclination angle of a swash plate and the strokes of pistons are adjusted. Thus the displacement of the compressor can be varied.
Japanese Unexamined Patent Publication No. 9-268974 discloses a variable displacement compressor of such type. The compressor has a suction chamber or a suction pressure region, a discharge chamber and a crank chamber or discharge pressure regions. The compressor also has a supply passage and a bleed passage. The supply passage interconnects the discharge chamber and the crank chamber. The bleed passage interconnects the crank chamber and the suction chamber. A control valve is interposed in the supply passage.
A yoke is connected to a valve housing at the middle of the control valve. A pressure sensing chamber is defined inside one end of the valve housing, and a bellows is provided in the pressure sensing chamber. A pressure sensing rod is fitted to the bellows. Suction pressure is applied to the bellows. As the suction pressure increases, that is, a heat load increases, the bellows contracts. The pressure sensing rod transmits expansion and contraction of the bellows to a valve body. A valve chamber is defined between the valve housing and the yoke, and the valve body is accommodated in the valve chamber. The valve body opens and closes a valve hole formed in the valve chamber.
The yoke includes a first yoke that connects with the valve housing and a second yoke that connects with the first yoke. A fixed core fits into the first yoke, and a plunger housing connects with the first yoke. A solenoid is held between the second yoke and the plunger housing. The fixed core is arranged in the plunger housing, and a movable core is accommodated in the plunger housing such that the movable core can approach the fixed core and separate from the fixed core.
An external controller supplies the solenoid of a solenoid mechanism with an electric current when necessary. Attraction between the cores varies with the magnitude of the electric current, and urging force for urging the movable core, that is, a load on the valve body varies. Force pressing the valve body in the direction to close the valve hole is adjusted. Thereby, a commencement point of the valve body for an internal control by the pressure in the pressure sensing chamber is adjusted. In such a state, as the suction pressure increases, the bellows contracts. Thereby, the valve body is moved in the direction to close the valve hole through the pressure sensing rod. On the contrary, as the suction pressure reduces, the bellows expands. Thereby, the valve body is moved in the direction to open the valve hole through the pressure sensing rod.
Meanwhile, the above-mentioned yoke is made of steel lumber such as a kind of aluminum killed steel SWCH12A and a kind of carbon steel S12C according to JIS, Japanese Industrial Standards. After assembling the yoke to the compressor, since the yoke is closed in the compressor, the yoke does not require rustproofing. However, upon manufacturing and assembling, the yoke requires rustproofing.
Also, since the plunger housing is previously brazed to the yoke, heat removes oil on the yoke upon brazing. Therefore, the yoke easily corrodes.
The yoke is conventionally treated by colored chromate zinc plating or rustproofing. Chromate treatment with hexavalent chromium is performed after zinc plating. Therefore, appearance and rust preventive performance of the zinc plating layer are relatively good.
An unwanted effect is that since the plunger housing previously connected to the yoke is made of stainless steel, plating with stainless steel (SUS) results in easily peeling. Therefore, after assembling the control valve, peeled plating layer may become foreign substances in the plunger housing, and may deteriorate sliding performance of the movable core. To solve the problem, for example, an elastic masking member caps the opening of the plunger housing before plating. This capping process causes manufacturing time and process of the control valve to increase. It is desired that the capping process is omitted and manufacturing time and process are reduced.
In accordance with the present invention, a control valve has a valve body for opening and closing a valve hole and a solenoid mechanism for urging the valve body by energizing a solenoid. The solenoid mechanism includes a yoke, a plunger housing, a fixed core and a plunger. The yoke accommodates the solenoid and forms a magnetic path. The plunger housing made of stainless steel connects with the yoke, and has a central axis. The fixed core connects with the yoke. The plunger is accommodated in the plunger housing and connects with the valve body. The plunger is attracted to the fixed core to move in the direction of the central axis by applying electromagnetic force from the solenoid. Black oxide treatment is performed to the yoke after the plunger housing is brazed to the yoke.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.